I see, somehow I thought that you had already tested all the resistors and diodes, hopefully that's all that's wrong. If that bridge rec. tested ok in circuit, no need to change it.
-
-
Check Q901, make sure none of the 3 pins are shorted to any of the others.Comment
-
I was about to test all of the capacitors, but while watching the video on testing the bridge rectifier, that other video listed on the right side of the YouTube screen caught my eye.
No short at Q901. I will put the good bridge rectifier back in since my new ones will not arrive until just before mid-March. The new resistors are expected to arrive on 2/20/2025.
Thanks for the tips!
Joe
Comment
-
Long story short, I got the new part in, and it also has continuity even before I installed it. I tried it anyways, and the LED quit working all together. So I put the old part back, and the LED came back. So I'm back to where I was before. I have not replaced the bridge rectifier.
In watching other power board repair videos, one mentioned the optocoupler and its role. So I looked up a video on how to test a optocoupler, and found this one:
https://www.youtube.com/watch?v=g7ZVk78MR7k
Per the video, putting the multimeter in diode mode, placing the red probe on pin 1 and the black probe on pin 2 should read about 1000. I get 851. If you reverse the probes, you should get nothing. I get 1015. Then when testing with the black probe on pin 4 and the red probe on pin 3, you should get nothing. I get 823.
I don't know if this is a valid test given the location of the component. But if it is, it implies that the optocoupler is faulty. Is this a valid test?
Here's a photo of the optocoupler in the power board:
Any help is appreciated!
Joe
P.S. - I leave tomorrow after for a week away. So I can't reply quickly.Comment
-
The optocoupler turned out to be fine.
I took the power board out of an identical working TV, and inserted the one I'm working on. The good TV did verify that it's a faulty power board. I did several measurements, and I can't find any difference as off yet. But, going back to testing the Stand-by voltage, I apparently measured the wrong wire. There is no clearly marked STANDBY pin on the connector. I used the DIM wire which appears to be incorrect, unless it is also used as a STANDBY.
Here's the pinout for the connector from top to bottom:
Pin 11: +12V
Pin 10: +12V
Pin 9:: GND
Pin 8: GND
Pin 7: +5V
Pin 6: +5V
Pin 5: +5V
Pin 4:: GND
Pin 3: GND
Pin 2: N/F
Pin 1: DIM
I "ASS"ume that N/F is On/Off?
The three +5V leads all go to a SP10100 Schottky Barrier Rectifier
The DIM lead goes to pin 4 (DIM) on the OZ99338GN Inverter Controller
The NF lead goes to pin 10 (ENA) on the OZ99338GN Inverter Controller
The two +12V leads go to pin 1 on a 8958A MOSFET
Here's a diagram on the components I mention:
The connector on the main board is as follows (12 pins, :
Pin 12: +12V
Pin 11: +12V
Pin 10: GND
Pin 9: GND
Pin 8: +5V
Pin 7: +5V
Pin 6: +5V
Pin 5: GND
Pin 4: GND
Pin 3: N/F
Pin 2: Not Connected
Pin 1: DIM
So this begs the question. Which pin is the STANDBY? I assume it has to be one of the +5V lines, but which one?
Joe
Comment
-
SchematicComment
-
Thank you for the great schematic version! Much better, and easier to read. It's also accurate versus the service manual.
I'm still trying to find the issue. Everything I've tested so far seems to test just fine when using the working power board as a baseline comparison for measurements. But I'm a patient learner, and realize that I will make mistakes as well. I also don't quit. I'll find it somewhere.
JoeComment
-
I took the time to install the good power board into the working TV and take power reads at the Main Board connector. I checked the power when "Plugged In", "Power On", "Mid Read" (if any), and "Resting Read". I then did the same with the bad power board installed. Below are the results. Notice the differences of the following - DIM, ON/OFF, all three +5v, and the two +12v reads (not that bad?). Something is pulling down the +5v, and messing with the DIM as well.
In looking at this general logic diagram graphic from a TampaTec YouTube video, after pressing the "Power' button (step 4), the Main Board sends power to the Power Board (step 5). Somewhere during and/or after step 5 is causing the problem.
I'm not sure what to look at on the power board next. All of the power going to the main board seems fine before the "Power" button is pressed. After that, it loses its mind.
All input is greatly appreciated!
Thank you!
Joe
Comment
-
Well if you are not finding any obvious differences in any voltages, redo the solder joints on bottom of board, many times they look good but can suffer from micro cracks.Comment
-
The difference seems to be the on off and maybe the dim, can try this, try with good board then bad board. test in usual way, neg probe on ground pos probe on the on/off pin, everything connected, tv in standby/plugged in but off, take note of reading, leave probe where it is turn tv on take note of reading. It looks like there's a problem right there.Last edited by nomoresonys; 03-06-2025, 03:24 AM.Comment
-
Don't worry about a "mid.read" it's not a factor here.Comment
-
Thank you for your reply. I will redo the solder joints as you suggested.
As for the testing, what you're recommending is actually exactly what I did to get the aforementioned measurements. I had the negative probe on ground, positive on the respective pin such as DIM or ON/OFF. While plugged in but not on, I took a read. Then I pressed the ON button and took a reading while the TV was trying to come up. I left the positive probe on the respective pin and took it's resting reading. I did not press the ON button again until I changed which pin I was testing.
But it's worth testing again to see if I get the same results.
And now my stupid question (I'm pretending I haven't asked one already). Below is a photo of two of the board components (I think they are transformers?). Is the discoloration of the two the sign of a problem?
Thank you!
JoeComment
-
I just repeated the testing. On the bad board, the "plugged in" readings were the same as before, 0 (zero) on both the DIM and ON/OFF pins. But, the resting readings (after pressing the ON button) for the DIM and ON/OFF pins are 0 (zero) on both now. This is a change on the DIM pin as it had a resting read of 1.58v after the first test. I tested each pin individually with the board plugged in, and then pressing the ON button. The +5v pins and +12v had the same results as before.
On the good board, nothing has changed as far as readings. Everything works great.
Back to the schematics!
Thank you!
Joe
Comment
-
I think you refer to standby as "resting" See how the power on voltage changes when you turn tv on with the good board, that's how it should be. The bad board doesn't do that. Most times that I have seen this tho, was because the mainboard wasn't sending the power on signal. But obviously your mainboard is good. I don't know what it could be, maybe the mainboard notices something wrong and doesn't send the on signal to powerboard?? This is an interesting problem, I bet one of these pros can solve it tho.
Comment
-
Last night I used the schematics to trace pin 4 (DIM) and pin 10 (ON/OFF) on the OZ9923 chip to see if any issues existed. I found no issues (shorts). Today I printed out the datasheet for the OZ9938 chip to learn more about the function of the other pins on the chip. Chip pins 5 and 6 deal with current/voltage sense feedback. It seems (logically only) as if the chip is not getting the feedback from the mainboard on the +5v lines. So I did some tracing of the +5v lines. All three +5v lines go back to the capacitor at C930, one of the Aluminum Organic Polymer Capacitors I have yet to replace. The replacement parts are scheduled to arrive today.
Will replacing it solve the problem? I don't know. But if the mainboard is not getting the feedback it expects, it's not going to start up (according to TampaTec). And the aforementioned capacitor has a role in the +5v.
During my tracing on the back of the board, I checked numerous things for shorts, and found nothing wrong.
We'll see what happens when I replace the Aluminum Organic Polymer Capacitor. I read that testing these type of capacitors is not the same as testing the other capacitors on the board, and that a Capacitance Resistance Inductance Digital LCR Multimeter is recommended.
I may be chasing the wrong thing, but I'm learning from the information that I have read, and the testing that I have done.
Joe
Comment
-
SOLVED!!! My first TV repair!
It was the Aluminum Organic Polymer Capacitor at C930 (680 10v). I replaced it this morning, and the TV came up immediately.
Thank you to everyone for your guidance and help!
Joe
Comment
-
Nice job congrats.
Comment
-
By the way, you can dirty test those caps the same way as the electrolytic caps.Comment
-
I thought I did and didn't find anything out of the ordinary. But maybe I didn't?
Thank you!
JoeComment
Comment